126 The Corpus Ponto-Bulbare 
were made on celloidin sections of tissue which had been fixed in formalin 
and mordanted in a double chrome salt. 
A section in any part of the ponto-bulbar body shows the free border 
of the nucleus outlined by a layer of nerve fibers cut either transversely 
as in Figs. 3, 4, 5, 6, and 7, or longitudinally as in Figs. 8, 9, 10, and 
11; in no case was there a stratum of cellular material on the surface. 
The diameter of these fibers, including their medullary sheath, ranges 
from 0.8 — 2 »; those making up the larger strands 1 — 2 p» thick, while 
those between the cells generally 0.8 in thickness. This small size makes 
the fibers easily distinguishable from the surrounding structures with 
which they come into close relation. ‘The fibers and cells together form 
a structure whose shape varies in section but the relation of cells to fibers 
are always such that masses of nuclear material he between the fiber 
bundles and the rest of the brain. Occasionally only do we find strata 
of cells between the fiber bundles as in Figs. 9 and 10. 
For the sake of simplicity it might be well in describing its finer 
structure to arbitrarily divide the ponto-bulbar body into a pontine part 
which fuses with the ventro-lateral surface of the pons, a middle part 
which extends median to the ventral cochlear nucleus and is perforated 
by the glosso-pharyngeal roots, and lastly a broad caudal part which over- 
laps the restiform body. With this in mind each part will be treated 
separately as was done in the gross description. 
In the region of the trigeminal nerve small strands of fine fibers sep- 
arate from the transverse fibers of the pons and turn caudally, forming 
rather compact small bundles which lie on the ventro-lateral surface of 
the pons just behind the root bundles of the fifth cranial nerve. The 
addition of fibers from the lateral side or middle penduncle is .compara- 
tively small, while the strands from the pons proper continue to turn in 
almost as far caudal as the emerging facial nerve. The nerve fibers grad- 
ually unite to form more or less rounded bundles which are spread out 
on the ventro-lateral border of the pons. Although there is this gradual 
increase of fibers from both sides, the cross section does not increase pro- 
portionately as it runs caudally. The reason for this is found to be due 
to rather large bundles of fibers which separate from the other fibers and 
run into the middle peduncle of the cerebellum. 
In the region of its most cephalic part, the ganglionic mass adjacent 
to the fibers is very small; but as it approaches the caudal border of the 
pons, it increases in amount, fusing so completely with the pontine nuclei 
that no sharp lne of demarcation can be drawn. This is well illustrated 
in Figs. 3 and 4, where the fibers, cut transversely, can be seen on the 
